Acoustic manipulation of micro-objects (particles, cells, bacteria) can be
achieved using ultrasonic standing waves in a fluidic or microfluidic
resonator. By matching resonator dimensions and acoustic field frequency it
is possible to use acoustic radiation force (ARF) to gather the particles in
the pressure nodal (or anti-nodal) plane, creating one or several
aggregates. In standard operating conditions, they are stable for as long as
needed in acoustic levitation at this position. In this study, we present a
new unexpected phenomenon. After creating an aggregate of light-absorbing
particles, we show that it is possible to force the breakup of the aggregate
when lighting it with an electromagnetic wave of adequate wavelength and
intensity. While the particles remain in levitation, they are rejected and
propelled away from the aggregate, leading to its destruction. We show that
this phenomenon depends on both amplitude of the ultrasonic field and
lighting intensity. Various experiments with different types of particles
and concentrations are used to discuss the possible phenomenon explanations.
Moreover, investigations showed that this phenomenon applies to biological
compounds such as red blood cells and stem cells, suggesting potential
biomedical applications.